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Great writeup, just a few things I've found with experience. Although the spark gap breaks over at ~350VDC, that doesn't mean the voltage can't go above that on occasion, Especially if you run 3V into the charger.

Also, that spark gap might wear out fairly quickly, so a SIDAC is the best option. That also answers your question about solid state replacments.

And thanks for the good photos on cutting down the board, I've got twenty or more of these boards, but I couldn't justify wrecking one for compactness.

Funny you should mention SIDACs I've been doing some rummaging and I've got some in the mail as we speak.

They trip at about the same voltage as the gas discharge tubes I'm using. I've also ordered more caps because although I said the one in the clip is 400V it's actually 1000V and thus larger than it strictly needs to be. Got some 400V 0.22uf caps coming so it should be possible to shave off a bit of weight and size

About the discharge tubes wearing out, it's not that fast.

I have run the circuit for half an hour straight with no failure plus a fair bit of time after that before a failure (lets see someone run an actual stungun for that long ).

I can't actually confirm it's the tube and not the coil that failed so the tube may be fine. Problem is the tube, coil and circuit are buried in very solid epoxy and I gave up trying to chip them out

Nothing else on the solid state front seems to be attractive, the other ones I was looking at were voltage clamping devices and thus don't perform the same massive dump as a spark gap or SIDAC will when it trips.

Well you could use say a SCR to trigger but for minimal parts and simplicity can't beat the one component triggering route.

I got all my boards from camera shops under the fairly broad reason of "a project", still have a basket of about 100 boards from a few years ago. Mind you, not all are the correct Kodak type to cut down to the tiny power square in the guide.

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Last edited by Hotwired on Fri Aug 12, 2011 9:12 am, edited 1 time in total.

So I make a topic called DIY stungun then only post a messy circuit connected with test leads.

Very bad of me.

So I'm working my way along to packing it up.

That's the driving circuit fixed to the coil and it's all powered by a 3V lithium CR123 battery (more like 3.8V fully charged).

On the incoming list is a sheet of PVC and a couple of small switches to make up a shell for it.

Expected dimensions for the entire functional device including battery are likely to be 60mm x 40mm x 30mm excluding terminals.

Clocked the circuit at a power consumption of ~3W.

Should really have put a resistor across the capacitor to drain it, I've had about three zaps so far from residual charge after the power was disconnected. Not comfortable but 0.22uf @ 350V isn't going to kill anyone. Hell, you get a worse shock off the 150uf @ 300V capacitor from the original camera circuit.

Had a small disaster while modding the coil and broke a secondary winding wire. It's important because the coil on this is actually two in series and that wire was joining them.

I'm still not 100% that it's fully connected or merely conducting through arcs, I had to flood an area with solder to try and force a connection to the extremely fine wire end embedded in epoxy because the wire was too fragile to extract enough to solder properly.

Like I said you can also break up the ignition system from small combustion engines such as small quad bikes, or similar.

The black coil here was from a mini-moto ignition system (an ebay example is here)

The rest of it is not required but you need to be careful breaking off the rest of the epoxy, circuitry and metal as the wires leading into the coil are NOT visible and need to be dug out of the solid epoxy resin carefully.

If you're totally screwed for places to get one then you could always buy enamelled wire and wind your own transformer.

Or of course you use the very common but much larger HV coil that everyone can get, a can sized ignition coil from a car engine.

not to be a d### but why waste time building your own ignition system if I got one of these (pdf. file) for less than 10$

if it can jump across the outside of the spark gap I think it's good enough for most uses[youtube]http://www.youtube.com/watch?v=nBc6nKt4iy0[/youtube]I am pretty sure you can find something like that locally

(the battery was low in that video... normally the rate of discharges is closer to 3 hz)